Many kinds of removable band-type couplings for pipes exist in the art. It is noted that throughout the specification and claims, the term “pipe” encompasses any kind of generally cylindrical object.
U.S. Pat. No. 6,293,556 to Krausz describes a coupling for connecting pipes of the same or different diameters. The coupling has a ring shaped seal made of rubber or other resilient material, constructed of a first ring seal seated over a second ring seal. The seals can be easily disconnected from one another to allow sealing against different diameter pipes. For smaller diameter pipes, both the first and second ring seals are used; for larger diameters, only one seal is used.
In the prior art, the seal for the larger diameter has an inner space which is in fluid communication with a fluid flowing in the pipe. The fluid that enters the inner space applies pressure to increase tightening of the seal. However, the second ring seal used for smaller diameter pipes does not have such an inner space.